The present invention relates to a new and improved construction of installation for charging or loading a multi-ply headbox for a papermaking machine, wherein at least two stocks diluted with water are infed in each case with the aid of an associated mixing pump to the headbox.
As is well known in the papermaking industry headboxes are used for producing a fiber web or fiber webs during the fabrication of multi-ply paper composed of at least two layers or plies have different material properties and/or different layer or ply thickness.
There are known in this technology a multiplicity of different constructions of multi-ply headboxes. By way of example reference is made to Swiss Pat. No. 619,777 and the corresponding U.S. Pat. No. 4,192,710 which describes a multi-ply headbox.
It is to be understood that the teachings of the present development are not limited to a special design of such type of multi-ply headbox. Within the headbox nozzle or flow channel there are arranged partition or separation walls which form within the channel of the headbox sub-channels or sub-passages for the different stock suspensions. The partition walls can be rigid walls or also flexible walls, for instance formed of plastic or thin sheet metal. Also, it is possible to design the partition walls so that a part thereof is rigid and another part is flexible, for instance at the end of the headbox channel.
Heretofore it was conventional practice to separately drive the mixing pumps of the infeed systems for the infeed of the individual stock suspensions to the headbox.
As is well known to those skilled in this art appreciable internal pressures, for instance in the order of up to approximately 2 to 10 bar, prevail within the headboxes. Now if during operation of a stock infeed system a mixing pump fails, for instance one of the mixing pumps is damaged, then the partition walls and, under circumstances, also the infeed channel walls within the headbox are exposed to high pressure differentials. These high pressure differentials can cause such walls to deform and possibly to become severely damaged, so that the headbox no longer is capable of properly operating. As a result, the entire production output of the papermaking machine is brought to standstill.